Conventionally, a p cladding layer is provided to improve emission performance by confining electrons in a light-emitting layer of a Group III nitride semiconductor light-emitting device. To enhance the effect of electron confinement, p-AlGaN having large bandgap energy is used as a p cladding layer. However, p-AlGaN needs to be grown at a low temperature to reduce thermal damage to the light-emitting layer, resulting in degradation of crystal quality. Therefore, a p-AlGaN/p-InGaN or p-AlGaN/p-GaN superlattice structure is used to suppress degradation of crystal quality. A p-AlGaN/p-InGaN superlattice structure is more preferable because p-InGaN exhibits superior crystal quality at a low growth temperature as compared with p-GaN.
Japanese Patent Application Laid-Open (kokai) No. 2005-51170 discloses that a superlattice structure in which p-AlGaN and p-InGaN are alternately deposited is used as a p cladding layer. It is also disclosed that p-AlGaN has a thickness of 1 nm to 5 nm and p-InGaN has a thickness of 1 nm to 5 nm.
Japanese Patent Application Laid-Open (kokai) No. 2007-80996 discloses that a superlattice structure in which p-AlGaN and p-GaN are alternately deposited is used as a p cladding layer. It is also disclosed that each of p-AlGaN and p-GaN has a thickness of at least one atomic layer.
However, when a p-AlGaN/p-InGaN or p-AlGaN/p-GaN superlattice structure is used as a p cladding layer, the overall thickness of the p cladding layer increases due to the presence of p-InGaN or p-GaN which does not contribute to electron confinement. This leads to a problem that the series resistance increases and the driving voltage increases.